In some motor vehicle climate control systems, a thermal-adsorption heat pump may be used instead of a compressor-driven heat pump. Thermal-adsorption heat pumps use an adsorbent chemical (e.g. zeolite, silica gel, activated carbons) rather than a mechanical compressor, and are driven by thermal energy (such as waste exhaust heat) rather than mechanical work.
One cycle of operation of a thermal-adsorption heat pump includes the adsorption of a refrigerant, e.g. water, onto a solid adsorbent, e.g. zeolite (during what is referred to herein as “adsorbing mode”), and the subsequent desorption of the refrigerant from the adsorbent (during what is referred to herein as “desorbing mode”). This process may occur in a canister referred to as an adsorber. During the adsorbing mode, the adsorbent is actively cooled, for example via a cool heat transfer fluid (HTF). The cooling of the adsorbent creates suction, which draws vaporized refrigerant into the adsorber and for adsorption by the adsorbent.
US 2011/0005267 describes an automobile air-conditioning system including a thermal-adsorption heat pump which operates in conjunction with a condenser and evaporator in the manner described above. The thermal-adsorption heat pump is powered by engine exhaust heat, and includes at least two adsorbers which adsorb and desorb refrigerant cyclically and asynchronously. In one embodiment, the system includes three working fluid loops: an HTF loop for heating/cooling the adsorbers where the working fluid is a mineral-oil-based HTF, an adsorption loop entirely exterior to the passenger cabin where the working fluid may be NH3, and a refrigerant loop transferring heat from the cabin to the adsorption loop (via an inter-loop heat exchanger) where the working fluid may be R-134a.
The HTF loop heats/cools the adsorbers to effect adsorption/desorption at the adsorbents within the adsorbers. Cool HTF for the adsorbing mode is provided by an HTF cooler, and hot HTF for the desorbing mode is provided by an HTF heater. Thermal reservoirs storing exhaust heat in phase change material (PCM) are coupled with the HTF heater. The adsorption loop includes NH3 which is adsorbed/desorbed from the adsorbents. After the engine is shut off, heat stored in the thermal reservoirs is used to desorb NH3 from the adsorbents into a reservoir. NH3 stored in the reservoir is then used to provide “surge cooling” after engine cold start, while HTF in the HTF loop is still being heated, in order to start thermally cycling the adsorbers and pumping refrigerant. To provide cooling to the cabin, a heat exchanger is coupled with the refrigerant loop and the adsorbent loop. At the heat exchanger, R-134a from the refrigerant loop condenses, while NH3 from the adsorbent loop evaporates. The refrigerant loop further includes an R-134a evaporator communicating with the cabin to provide cooling to the cabin via a blower.
In contrast with the above-described system, the inventors herein have identified a climate control system incorporating a thermal-adsorption heat pump which provides cabin heating in addition to cabin cooling, despite requiring fewer engine-driven or electrically-driven components. That is, the inventors herein have recognized that in a two-adsorber system, wick chambers (such as those used in heat pipes) thermally coupling each adsorber with a respective antifreeze tank may be used in place of a dedicated evaporator and condenser. In one example, a method for a vehicle cabin climate control system includes, during engine operation, asynchronously switching first and second adsorbers of a thermal-adsorption heat pump between adsorbing and desorbing modes, the adsorbing adsorber cooling antifreeze via wick chambers and the desorbing adsorber heating antifreeze via wick chambers, and conditioning cabin air via the heated antifreeze or the cooled antifreeze depending on an operating mode of the climate control system.
In this way, when an adsorber is in the adsorbing mode, the suction of a refrigerant (e.g., water, NH3, R1234f) stored in the wick chambers engenders a cooling effect in the antifreeze tank in which a portion of the wick chambers are disposed. This cooling effect can be harnessed to cool the passenger cabin during hot weather conditions (for example during a “summer mode”). Similarly, when an adsorber is in the desorbing mode, the condensation of refrigerant desorbed from the desiccant in the wick chambers engenders a heating effect in the antifreeze tank, which may be harnessed to heat the passenger cabin during cold weather conditions (for example during a “mild winter mode” or “severe winter mode” depending on the severity of the cold weather).
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.